Time and tide wait for no man – Geoffrey Chaucer
STRUCK BY THE MOON
The transition from the brightness of a full moon to the darkness of a moonless night has fascinated peoples and influenced beliefs throughout history. The rhythms of the lunar cycles remain a vital reference for many cultures all over the world. Since the most ancient times, people have observed the waning and waxing of the moon and used these regular cycles to mark time. Even today, many cultures and religions follow the lunar calendar and attach important celebrations and customs to particular phases of the moon. Multicultural Indonesia is no exception and most religions practiced in the country greatly value the position of the moon in the sky.
The Islamic and Hindu religions as well as the traditional Chinese culture follow different versions of a full or partial lunar calendar that determines the dates for religious festivities. For Muslims, the first day of the month corresponds to the rising of the new moon, and the Islamic calendar (or Hijri calendar) is a purely lunar calendar. The Balinese New Year, Nyepi, falls on the day after the dark moon of the spring equinox and also Christians follow the lunar cycles to determine when to celebrate Easter. In Indonesia, Vesak day – or the day the birth, enlightment and death of Gautama Buddha – is established by the Chinese lunar calendar; in Animist practices, certain days in lunar phases are considered particularly auspicious.
LUNAR INFLUENCE ON MARINE LIFE
As the moon waxes and wanes, and the tide ebbs and flows, many intertidal organisms meet and mate, breed and hatch, making the cyclical changes of the moon-phases and water levels an essential component of their life cycles. The lunar and tidal cycles affect the rhythm of life in many marine organisms where variations in environmental cues, such as light and tide levels, appear to influence their movement and behaviour. In fact, many animals’ biological rhythms tend to occur at regular intervals, in sync with cycles observed in nature. They are able to track these cyclic motions endogenously via a range of different mechanisms, allowing them to anticipate essential activities, such as reproduction. For instance, many animals tend to spawn during periods of high tides to increase chances of survival while others opportunistically forage near the surface when the tides are low. Those that are subject to large fluctuations in temperature and exposure, such as organisms in the intertidal zone, adopt different feeding and life-history strategies in response to the extreme conditions. The regular flow of the tides creates a zone that is cyclically submerged by water or exposed to the sun according to the height of the tide. This is the intertidal or littoral zone and supports a rich variety of life forms. Different kinds of plants and animals benefit from changes in the water level and occupy the zone at different times accordingly. At high tide, the area is inhabited by aquatic creatures attracted by the nutrients and plankton brought in by the water. At low tide, the “shift” changes and many terrestrial animals come to feed in the flats or in the shallow pools.
Many large fish species group together at particular times of the year to reproduce, forming the so-called spawning aggregations. Although specific reproductive habits differ according to the species and region, fishes usually meet at the same time and in the same place each year, often according to the moon phases. Some travel long distances to get to the “reproduction meeting” on time! In Epinephelus sp., it has been observed that, during the spawning period that occurs from May to June, the quantity of eggs released in the water is higher before and after the new moon and is low near the full moon.
Corals are sessile animals, which means they are permanently attached to the substrate and not free-moving. This poses a challenge to fertilization; this is why some corals simultaneously release eggs and sperm in the sea. This event is known as “the mass synchronous coral spawning” and it takes place once a year. For a few nights after the full moon, the sea is filled with gametes (eggs from the female) and clouds of sperm that drift in the water. After fertilization, currents carry the eggs to other areas, where the larvae will attach to the substrate and form new colonies of corals.
When the shore is exposed during low tide, living conditions become extreme. Few animals can tolerate the increasing heat, salinity and lack of water typical of an intertidal zone at low tide. Many move to deeper water or inland and wait for the tide to come back. But not all can move. For instance, sea anemone expand and contract according to the inflow of water. When the tide is low, sea pens retract into the sand and sea anemones fold their tentacles inward. When the water is up, they expand completely, resembling to beautiful underwater flowers with open petals.
Local Legend: Pau Amma and the cause of the tides
According to Malay/Indonesian folklore, the centre of the ocean is the place where all the waters of the Earth are collected and where Pau Amma, the giant crab, lives in isolation. This crab is the biggest of all creatures and twice a day it goes out to look for food. When it leaves its cave, all the waters of the seas and the rivers flow inside, causing the tide to ebb. When Pau Amma returns home, the tide rises, because the giant crab blocks the entrance to the inflowing waters with its massive body. And so it goes, the water ebbs and flows, as the giant crab goes back and forth looking for food.
Bahasa fast facts
In Bahasa Indonesian, BULAN means moon, but it also means “month”, while PURNAMA, meaning “full moon” is a first name both for men and women and originally comes from Sanskrit पूर्णिमा (purnima).